Semiconductor Solar Cells:
A Path to Higher Performance Photovoltaic Energy Sources
for Terrestrial and Space Applications
J. Guido, Associate Professor
Department of Electrical and Computer Engineering
Department of Materials Science and Engineering
Virginia Polytechnic Institute and State University, Blacksburg,
Slides (2.9 MB PDF)
Photovoltaic technology holds great promise as a sustainable,
environmentally friendly energy source for the 21st century.
While photovoltaic devices (solar cells) currently provide
a miniscule percentage of the world's energy needs, it
is a surprisingly large and rapidly growing industry.
The global market has been growing at over 30% annually
since the late 1990's, and now generates over $4.5 billion
U.S. in annual revenue. This rapid growth is expected
to continue into the foreseeable future driven by world-wide
interest in developing clean, renewable energy sources.
III-V semiconductor devices have already demonstrated
one-sun efficiencies over 30%; however, they are expensive
because different semiconductor materials must be grown
on single-crystal GaAs or Ge substrates while maintaining
good lattice matching to assure long minority carrier
lifetimes. An alternative methodology involves semiconductors
such as CdTe and CuInGaSe2 which exhibit strong optical
absorption and acceptable electronic properties even when
deposited as polycrystalline films on large-area, low-cost
(glass or metal) substrates. Such thin-film solar cells
have a favorable cost structure; however, after more than
twenty years of research activity, the power conversion
efficiencies of high-volume production devices remain
well below 20%.
generation solar cell R&D aims to combine both high
power conversion efficiency and low-cost manufacturing
in the same photovoltaic technology. Nitride semiconductor
alloys show promise as the material of choice for 3rd
generation solar cells. Single-crystal quaternary alloys
such as BGaInN or BGaNAs with lattice matching to GaN
could prove to be a good choice for terrestrial applications
at very high solar concentration and space-based power
generation for missions operating closer to the sun. Amorphous
ternary alloys such as GaInN or GaNAs could lead to high-efficiency,
multi-junction solar cells with low manufacturing costs.
The feasibility of these new solar cell technologies will
be argued on the basis of known materials parameters,
proof-of-concept devices reported in the literature, and
ongoing and future work at Virginia Tech.
joining Virginia Tech in 1999, Louis J. Guido was
a Member of Technical Staff at AT&T Bell Laboratories
from 1982 until 1984. During that time he earned his M.S.
degree in Electrical Engineering from the University of
Illinois. He returned to the U of I in 1985 to conduct
independent research and received his Ph.D. degree during
the spring of 1989.
that year, Dr. Guido joined Yale University as an Assistant
Professor in the Department of Electrical Engineering.
In 1992, he was one of 15 engineers nationwide to be awarded
a five-year NSF Presidential Faculty Fellowship. In 1993,
Dr. Guido was promoted to Associate Professor at Yale
U and awarded the John J. Lee Endowed Chair in Electrical
Engineering. He was elected a Senior Member of the IEEE
Guido joined Virginia Tech in 1999 as an Associate Professor
with a joint appointment in the Departments of Electrical
and Computer Engineering and Materials Science and Engineering.
He was named a VT College of Engineering Faculty Fellow
in 2004. Dr. Guido was an IEEE Electron Devices Society
Distinguished Lecturer from 2000 to 2004.
research interests include the physics of photonic devices
operating at short (UV) and long (FIR) wavelengths; the
physics of high-power, high-frequency electronic devices;
and the synthesis and characterization of compound semiconductor
alloys and quantum structures. Dr. Guido's overall work
on III-V semiconductor thin-film synthesis and device
physics has contributed to 50 journal articles, which
have been cited more than 1,100 times to date according
to the ISI Web of Science; 50 conference papers; and 30
invited seminars at leading national and international
research universities and industrial laboratories.
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